Photolysis of dimethylsulfide in the northern Adriatic Sea: Dependence on substrate concentration, irradiance and DOC concentration

The influence of dimethylsulfide (DMS) and DOC concentrations and varying irradiance levels on the photolysis of DMS was evaluated. Laboratory experiments were conducted with 0.2 μm filtered aged seawater from the northern Adriatic Sea and artificial radiation. Photolysis of DMS followed pseudo first-order kinetics with the photolysis rate constant k directly dependent on irradiance intensity. Photolysis rates of DMS were also directly dependent on DOC concentration. In field experiments using natural solar radiation, DMS (5 nM initial conc.) was removed from freshly collected 0.2 μm filtered seawater at rates of 0.6 ± 0.1 nmol l^-1 h^-1, equivalent to k = 0.12 ± 0.02 h^-1. Based on these photolysis rates and using in situ profiles of downwelling irradiance, DMS and DOC concentrations, we calculated a water-column-integrated DMS removal rate due to photolysis of 165 ± 20 μmol m^-2 d^-1. Averaged over the entire water column, the photochemical turnover time of DMS was 3.1 ± 0.5 days. Most (88%) of the DMS was photolyzed in the top 10 m of the water column. Comparison of our data with photochemical and biological turnover rates published elsewhere indicates that photolysis may be an important sink of DMS in shallow coastal waters.